Measurements of the magnetic field, either the vector field or its magnitude, taken at the sea floor can be used to make inferences regarding the presence and motion of objects that impart a magnetic field disturbance. Systems derived from such sensors can be broadly termed magnetic anomaly detection or magnetic tracking systems. From a suitable suite of such sensors the magnetic moment and a set of parameters characterizing its track can be used to predict the object's motion through the volume, yielding valuable information. For this reason it is useful to know the minimum attainable variance that a given suite of sensors can provide regarding a given vessel's magnetic signature and track. This type of analysis can further serve to illuminate the minimum required spacing of sensors in a domain and the signal fusion and processing functions necessary to meet a certain accuracy of track. Related issues associated with for instance, the communication demands on distributed and networked configurations of such sensors can only be adequately addressed with an accurate assessment of the vessel track variance as a function of the number of sensors and their spatial configuration.
If the attainable vessel track accuracy is not adequately understood, systems could be designed from excessively sparse configurations leading to grossly inadequate track information. This could imply excessive false alarm rates and increased communication network demand for a distributed sensor field. Poor track information can additionally render the system unusable to secondary and more valuable surveillance assets. Excessively pessimistic assessments of track accuracy would lead to more deployed sensors than necessary resulting in a greater cost and time of deployment and an unfounded prohibition against the use of such sensors.
Measurements of the local magnitude of the magnetic field, so called “total-field” measurements allow for the exploration of a number of distributed sensor surveillance system designs and sensor signal processing issues. Total field magnetic sensors are relatively insensitive to sensor motion and therefore offer some advantages in rapidly deployed systems.
There is a current need for tools and methods that determine the amount of information that a sparse suites of magnetic sensors can provide regarding transiting vessel size and track in realistic undersea noise environments, as well as signal processing algorithms that operate in a hierarchical framework for data fusion across sparse sensor suites so that necessary information sharing is accomplished to meet a requisite track and moment accuracy with a minimal inter-sensor communication cost as envisioned in distributed networked undersea sensor concepts for ASW.